Royal Knifefish Care Guide - Aquarium Notes, Diet & Breeding

The Royal Knifefish is a spectacular giant featherback with an elongated, laterally compressed body and a long undulating fin running beneath the body. Its silvery to bronze-brown colouration is marked by dark, irregular blotches and bands, giving each fish a dramatic pattern as it moves through the water. The mouth is large and adapted for capturing sizeable prey.

Royal Knifefish are native to the Mekong basin of mainland Southeast Asia, including parts of Thailand, Laos and Cambodia. They inhabit large rivers, deep channels, floodplain areas and connected habitats across the lower and middle Mekong region.

Royal Knifefish are unsuitable for ordinary home aquariums once they begin approaching adult size. A responsible long-term setup should provide at least 1,000 litres, with an adult enclosure ideally around 300 cm long, 100 cm wide and 100 cm high or larger; substantially bigger systems are preferable. Use a tightly secured lid because these powerful fish can escape, leave broad open swimming areas, and include shaded retreats made from large pieces of driftwood, rockwork or robust aquarium structures. A smooth sand or fine-gravel substrate is safest, and filtration must be powerful while avoiding excessively turbulent flow.

Up to about 120 cm (47 inches) in total length in the wild, although aquarium specimens are often smaller. Males and females are not known to show a dependable difference in maximum size.

This species is a carnivorous predator. Offer a varied diet of appropriately sized pieces of fish, prawns, mussels, earthworms and other meaty foods, with whole frozen or fresh aquatic foods used where practical. Young fish generally need smaller offerings more often, while adults can take large meals at suitable intervals. Avoid relying on live feeder fish, which can introduce parasites and provide an unbalanced diet.

Royal Knifefish are predatory and should only be housed with very large, robust fish that are too big to swallow and are not prone to fin-nipping or harassment. Suitable companions may include large peaceful catfish, oversized barbs and other substantial Mekong or Southeast Asian river fish, provided the aquarium is large enough for all of them. Small community fish, shrimp and ornamental invertebrates will be treated as prey, while aggressive cichlids and similarly territorial knifefish are poor choices. Adults may also become intolerant of other large knifefish.

Royal Knifefish are rarely bred in home aquariums, largely because adults become extremely large and require spacious breeding facilities. They are believed to spawn as a pair, depositing adhesive eggs on a submerged surface such as wood, with the male probably guarding and fanning the clutch. Successful attempts require excellent water quality, a mature compatible pair, substantial cover and a very large aquarium or pond; reliable captive-breeding information for this species remains limited.

Royal Knifefish show little reliable external sexual dimorphism. Mature females may become fuller-bodied when carrying eggs, but body shape alone is not a dependable way to sex them; mature males and females are generally distinguished more reliably during breeding examination.